In a 3-l. three-necked, round-bottomed flask, fitted with a mechanical stirrer and mercury seal, a 500-cc. separatory funnel, and an efficient reflux condenser, is placed 61 g. (2.5 atoms) of magnesium turnings or powder(Note 1). The magnesium is then covered with 200 cc. of anhydrous ether. About 5 cc. of pure tert.-butyl chloride (with a crystal or two of iodine) is added to start the reaction. Stirring is begun, and a solution of 227 g. (2.5 moles) of pure tert.-butyl chloride(p. 144) in 1100 cc. of anhydrous ether is dropped slowly (Note 2) on the magnesium during six to eight hours. The reaction is practically complete when all the halide has been added, but stirring should be continued for fifteen minutes longer.

The reaction mixture is now surrounded by an ice and salt mixture. The separatory funnel is replaced by a two-holed rubber stopper containing a thermometer (bulb immersed in the reaction mixture) and a glass tube the outer end of which is connected to a mercury trap(Note 3). When the temperature of the reaction mixture has fallen to 0°, the condenser is replaced by a tube 10 mm. in diameter and adjusted so the end is 50 mm. above the surface of the reaction mixture. The reaction mixture is stirred and carbon dioxide is added through this tube directly from a cylinder after passing through two bottles containing concentrated sulfuric acid. The carbon dioxide is added as rapidly as it is used up. The temperature is controlled by the rate of stirring and should not go above 8+°. After two and one-half to three hours the temperature falls below 0°. Then the addition is continued for one-half hour under an excess pressure of 45 mm. (Note 3). The temperature falls to −3 to −5° at the end of this time, and the reaction is complete.

After the flask is surrounded with ice, the reaction mixture is hydrolyzed (Note 4) with 25 per cent sulfuric acid, transferred to a 2-l. separatory funnel, and then the ether layer is separated (Note 4). The water layer is extracted with four 100-cc. portions of ether. The combined ether extracts are then washed with four 100-cc. portions of 25 per cent sodium hydroxide solution to remove the trimethylacetic acid from the ether.

The aqueous alkaline extract is heated to 100° to remove ether and volatile impurities. The solution is then cooled with ice and acidified with 25 per cent sulfuric acid, and the organic acid separated. The water layer is distilled from a 2-l. flask until no more oily solution comes over. The distillate is saturated with salt, and the acid layer is separated. This water layer together with the low-boiling fraction from distillation of the crude trimethylacetic acid is distilled and the distillate salted out as before.

The combined acid layers are distilled from a 250-cc. Claisen flask connected to an air condenser, which in turn is connected to a side-arm flask cooled by running water. The trimethylacetic acid is collected at 162–165°/atm. press., 110–112°/124 mm. The yield, which depends somewhat on the form of magnesium, is 157–162 g. (61–63 per cent of the theoretical amount based on tert.-butyl chloride) when ordinary magnesium turnings are used and 177–178 g. (69–70 per cent) when 200-mesh magnesium powder is used. The acid melts at 34–35°.

2. Notes

1.
The yield of product depends to a considerable extent upon the form of magnesium used. Either the finer commercial grade of turnings should be used or the 30- to 200-mesh powdered magnesium that is kept in a tightly stoppered bottle when not in use. The powdered magnesium makes possible a 5–8 per cent increase in yield.

2.
The rate of addition of the halide solution is important. The slower the rate, the better the yield. A delivery constant of the separatory funnel should be determined so that the solution can be added uniformly over a period of six to eight hours. A modified procedure for preparing tert.-butylmagnesium chloride has been described by Whitmore and Houk.1

3.
The mercury trap enables the operator to adjust the flow of the carbon dioxide according to the rate of absorption, and to apply a pressure of 45 mm. during the last half-hour. The pressure itself has practically no effect. The trap consists merely of a narrow glass test tube containing mercury, and the tube is made to extend beneath the surface.

4.
The hydroylsis of the reaction mixture and subsequent separation of the acid is the procedure given on p. 362. Sulfuric acid should be added during the hydrolysis as long as any particles of magnesium are present. The water layer does not become clear, owing to solidification of the organic acid.

[(B) (from Pinacolone)]

Submitted by L. T. Sandborn and E. W. Bousquet.

Checked by F. C. Whitmore and T. Otterbacher.

1. Procedure

In a 5-l. round-bottomed flask fitted with a mechanical stirrer is placed a solution of 330 g. (8.25 moles) of u.s.p. stick sodium hydroxide in 2.8 l. of water, and the solution is cooled to 0° in an ice-salt bath. To the well-stirred solution 480 g. (154 cc., 3 moles) of bromine is added from a separatory funnel at such a rate as to keep the temperature below 10° (Note 1) (fifteen to twenty minutes). The solution is cooled again to 0°, and 100 g. (1 mole) of pinacolone(p. 462) is added from a separatory funnel, the temperature being kept below 10°. After the solution is decolorized (about one hour) it is stirred for three hours at room temperature.

The flask is then fitted with a separatory funnel and a condenser for distillation, and heated with a Meker burner to steam-distil the bromoform and carbon tetrabromide(Note 2) and (Note 3).

The burner is then removed, the mixture is cooled to 50°, and 400 cc. of concentrated sulfuric acid(Note 4) is added through the separatory funnel. The heat of neutralization causes some trimethylacetic acid to distil with water. When all the acid is added the flask is heated again and the trimethylacetic acid comes over with about 400 cc. of water. When all the trimethylacetic acid (70–80 cc.) has distilled, a liquid heavier than water begins to come over. The distillation is stopped and the acid separated from the water in a separatory funnel and dried either with calcium chloride or by distilling with benzene which carries over all water (Note 5). The trimethylacetic acid is further purified by distillation under reduced pressure. It boils at 75–78°/20 mm.; melts at 34–35°; and the yield is 63–65 g.

The water layer is extracted with two 100-cc. portions of ether. The combined ether solutions are dried with calcium chloride, the ether distilled, and the residue fractionated under reduced pressure, using a modified Claisen flask(p. 130). Ten to twelve grams may be obtained in this way. The total yield is 72–75 g. (71–74 per cent of the theoretical amount).

2. Notes

1.
The temperature must be kept low during the reaction to prevent formation of sodium bromate.

2.
The reaction between sodium hydroxide and tribromopinacolone is not complete at room temperature. Heating in this manner, rather than separation in the cold, results in an increase of 10–15 per cent in the yield.

3.
The bromoform passes over with the steam rather rapidly. In some runs some carbon tetrabromide was also obtained. Toward the end of the steam distillation a heavy oil that is more or less of a lachrymator may come over. This is undoubtedly brominated pinacolone. The bromoform may be purified by distillation under reduced pressure. One run gave 115 g. of product, boiling at 78–79°/22 mm.

4.
An equivalent amount of hydrochloric acid may be used without affecting the yield.

5.
The trimethylacetic acid is dried very easily by distilling with about 50 cc. of benzene at ordinary pressure until all the water is removed, and then the residue is distilled under reduced pressure.

3. Discussion

Trimethylacetic acid can be prepared by the hydrolysis of tert.- butyl cyanide;2 by the oxidation of dimethyl-2,2-propanol with chromic acid;3 by the oxidation of pinacolone with sodium hypobromite,4potassium hypochlorite,5 and chromic acid;6 by the carbonation of tert.- butylmagnesium chloride;7 and by treatment of butanol,8isobutanol,8 or acetone9 with carbon monoxide at high temperature and pressure.

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